Small, low power, and high performance (low vibration sensitivity, low temperature drift, and low phase noise) oscillators are needed for a number of GPS, radio, and radar systems. Furthermore, cell phones and computer boards also are in need of highly stable clock and timing references for analog and digital processing. As phones and computer systems expand into multi-frequency operational modes, the need for multiple clock frequencies with low power requirements increases. This in turn increases the interest in small banks of low power oscillators that can replace higher power frequency synthesizers.
Typically, quartz-base oscillators are constructed using hybrid techniques. That is the quartz resonators are fabricated on a small single piece of quartz (typically about 1 inch square), tested, and mounted in a ceramic package with a surface mount circuit card using various epoxies containing conductive materials. The conductive epoxies used provide both mechanical and electrical connections to the resonator with low stress. Since no handle wafer is used in these fabrication processes, the resonators need to be thick enough so as not to break during the handling and mounting processes. Since the frequency is inversely dependent on the thickness for shear-mode devices, this means that frequencies above about 100 MHz (or quartz thicknesses below about 10 microns) have proved difficult to manufacture in this manner. In addition, for UHF operation, the resonator dimensions are significantly smaller than larger devices. This reduces the resonator's equivalent circuit parameters and increases the susceptibility of the circuit to stray capacitances. Typically, the intrinsic capacitance of UHF resonators (C0) is in 0.1 pf range, and this requires that parasitic capacitances are below about 0.01 pf in order for them to not affect the operation of the oscillator. Thus, there is needed to reduce the stray signals to manageable levels.
According to the present disclosure, it is possible to integrate a resonator with active electronics to form a small, low power, and high performance (low vibration sensitivity, low temperature drift, and low phase noise) oscillator with reduced stray signals.
In the following description, like reference numbers are used to identify like elements. Furthermore, the drawings are intended to illustrate major features of exemplary embodiments in a diagrammatic manner. The drawings are not intended to depict every feature of every implementation nor relative dimensions of the depicted elements, and are not drawn to scale.